The present invention relates generally to a step motor and more particularly to an improved drive control circuit for a step motor, i.e., an accommodation circuit for converting to one-phase or half-step operation.
Step motors are used in many applications to provide incremental movement or "stepping". A common application is in electronic typewriters. With depression of a key, the step motor advances the paper-carrying carriage (or the typing mechanism) one step. Depression of the carriage return causes the step motor to rapidly move the carriage (or the typing mechanism) to a "return" position, set by the margin control.
Step motors include a stator and a rotor. As the phase windings of the stator are sequentially energized, the rotor responsively rotates in the prescribed manner. Energization is accomplished by interconnection of the prescribed phase winding with a motor drive supply. This interconnection is sequentially controlled by a logic sequencer in response to a clock. The logic sequencer provides a series of energization signals, and the power drivers, respectively associated with each winding, responsively interconnect the windings and the motor drive supply.
Normal operation of the step motor is two-phased. That is, each stator winding is sequentially energized for two clock periods and de-energized for the following two clock periods. However, in various applications of a step motor, it is desirable to convert the energization pattern and thereby change the operational mode of the step motor. The two primary alteratives are one-phase and half-step operation.